The growth and differentiation of epidermal cells derived from normal human tissue and from patients with a variety of dermatological diseases will be compared with a combination of cell culture and biochemical techniques in order to answer the following questions: (1) Is each pathological condition due to an intrinsic abnormality in epidermal cells? (2) If it is, what are the defects at the cellular level in terms of epidermal growth and differentiation? (3) What are the defects at a molecular level in terms of keratins and other cellular proteins.